RW: We quote a prison psychiatrist who spent 25 years talking to really violent men, and he says he has yet to see an act of violence which was not caused by people feeling disrespected, humiliated, or like they've lost face. Those are the triggers to violence, and they're more intense in more unequal societies, where status competition is intensified and we're more sensitive about social judgments.

BJ: Once we become aware of the impact of inequality on all of these social ills, what do we do about it?

RW: Countries seem to get their greater equality in quite different ways. Sweden, for example, uses the big government way: There are very big differences in earnings, which are redistributed through taxes and benefits. It has a large welfare state. Japan, on the other hand, has smaller income differences to start with, does much less redistribution, and doesn't have such high social expenditure. But both countries do very well—they're amongst the more equal countries and their health and social outcomes are very good.

What we've learned is that the real quality of life for all of us now depends on improving the social environment, and that we have a policy handle on how to do that. It's not that we all need to have more therapy to try and make us nicer people. Income distribution, an issue government or big corporations can do something about, really affects the psychosocial well-being of the whole society. But we can't just rely just on taxes and benefits to increase equality—the next government can undo them all at a stroke. We've got to get this structure of equality much more deeply embedded in our society. I think that means more economic democracy, or workplace democracy, of every kind. We're talking about friendly societies, mutual societies, employee ownership, employee representatives on the board, cooperatives—ways in which business is subjected to democratic influence. The bonus culture was only possible because the people at the top are not answerable to the employees at all.

Not exactly, says British epidemiologist Richard Wilkinson.

For decades, Wilkinson has studied why some societies are healthier than others. He found that what the healthiest societies have in common is not that they have more—more income, more education, or more wealth—but that what they have is more equitably shared.

In fact, it turns out that not only disease, but a whole host of social problems ranging from mental illness to drug use are worse in unequal societies. In his latest book, The Spirit Level: Why More Equal Societies Almost Always Do Better, co-written with Kate Pickett, Wilkinson details the pernicious effects that inequality has on societies: eroding trust, increasing anxiety and illness, encouraging excessive consumption.

In most Chinese cities couples are usually allowed to have only one child—the policy in its pure form. But in the countryside, where 55% of China’s population lives, there are three variants of the one-child policy. In the coastal provinces some 40% of couples are permitted a second child if their first is a girl. In central and southern provinces everyone is permitted a second child either if the first is a girl or if the parents suffer “hardship”, a criterion determined by local officials. In the far west and Inner Mongolia, the provinces do not really operate a one-child policy at all. Minorities are permitted second—sometimes even third—children, whatever the sex of the first-born (see map).

The provinces in this last group are the only ones with close to normal sex ratios. They are sparsely populated and inhabited by ethnic groups that do not much like abortion and whose family systems do not disparage the value of daughters so much. The provinces with by far the highest ratios of boys to girls are in the second group, the ones with the most exceptions to the one-child policy. As the BMJ study shows, these exceptions matter because of the preference for sons in second or third births.

For an example, take Guangdong, China’s most populous province. Its overall sex ratio is 120, which is very high. But if you take first births alone, the ratio is “only” 108. That is outside the bounds of normality but not by much. If you take just second children, however, which are permitted in the province, the ratio leaps to 146 boys for every 100 girls. And for the relatively few births where parents are permitted a third child, the sex ratio is 167. Even this startling ratio is not the outer limit. In Anhui province, among third children, there are 227 boys for every 100 girls, while in Beijing municipality (which also permits exceptions in rural areas), the sex ratio reaches a hard-to-credit 275. There are almost three baby boys for each baby girl.

Ms Das Gupta found something similar in India. First-born daughters were treated the same as their brothers; younger sisters were more likely to die in infancy. The rule seems to be that parents will joyfully embrace a daughter as their first child. But they will go to extraordinary lengths to ensure subsequent children are sons.